The invention relates to a method for the manufacture of contacts between electrochemically active discs and interconnectors in planar high temperature fuel cells. It also relates to a fuel cell battery having such contacts. The fuel cells are solid oxide fuel cells (SOFC, Solid Oxide Fuel Cells) which operate at temperatures between 700° C. and 950° C. The interconnector separates an air side from a gas side and establishes an electrical connection between adjacent fuel cells.
A battery of planar fuel cells includes a stack of cells, in which alternating plate-like interconnectors and electrochemically active discs, so-called PEN elements (discs with three layers: positive electrode-electrolyte-negative electrode), are arranged. The interconnectors are also termed a bipolar plate. They provide discrete contacts in the form of pimples or webs between the electrodes of adjacent PEN elements. The pimples for example form a special pattern in which the pimples all have the same form and a grid-like arrangement having a density of at least 10 pimples per cm2. For a good degree of efficiency of the fuel cell battery with minimal ohmic losses a contacting of the PEN elements with the interconnectors is required which has a uniformly low electrical resistance. In accordance with a known method the contact layer is manufactured from a paste which is a mixture of a powder-like electrically conductive material and a liquid (see for example US 2007/003819 with the title “Electrically Conductive Fuel Cell Contact Material). A contact mixture of this kind can be applied by means of screen printing, slip spraying or slip rolling onto the electrodes or onto contact surfaces formed by the pimples or webs. After an assembly of the cells to form a stack, solid connections between the contact surfaces and the electrodes arise out of the contact mixture by drying and firing. During this assembly the paste that is applied is kept moist in order to be able to compensate for differences in height of the pimples and webs. It has, however, now been shown that the assembly of the cell stack leads to partly insufficiently formed inhomogeneous connections. As a result of this deficiency, cell voltages are measured at the cells of the assembled stack which are of different sizes and which signify ohmic losses which are not ideal. A reduction of the tolerances during the manufacture of the interconnectors cannot be considered for cost reasons.